Track 4 · Messaging and Correctness
Design Live Comments (Hotstar / JioCinema Match Chat)
Two crore people are watching an IPL final and the chat panel is open on every phone. You cannot show every comment to every viewer, and you should not try. The design is about choosing what to drop, how to push the rest, and how to replay it later against the video timeline.
Interview problem28 min read
On this page
- Problem framing
- Questions I ask before drawing anything
- Requirements
- Estimation
- API
- Data model
- Building it up
- SSE: why this transport
- The fan-out tiers
- Choosing five comments out of ten thousand
- Ordering and timestamps
- Reactions: counters, not messages
- Rate limits and abuse
- Moderation without making the chat slow
- VOD sync: replaying the chat against the video
- Failure modes
- Interview Leveling Rubric